Galvanometer damping arrangement using adjustable volume fluid damping



United States Patent 3,404,342 GALVANOMETER DAMPING ARRANGE- MENT USING ADJUSTABLE VOLUME FLUID DAMPING Harry R. Allen, Jr., Littleton, C0lo., assignor to Honeywell Inc., Minneapolis, Minn., a corporation of Delaware Filed June 15, 1965, Ser. No. 464,041 4 Claims. (Cl. 324-125) A general object of the present invention is to provide a new and improved galvanometer construction which exhibits an improved frequency response throughout a wide frequency range.

The invention relates to a galvanometer of the type utilized in seismographs, oscillographic recorders, and the like and, more particularly, to an improved galvanometer characterized by its improved frequency response in the overall frequency range and embodying an improved damping arrangement in which the damping may be adjusted to suit the requirements of the galvanometer while maintaining the vibratory assembly thereof totally immersed in a damping media.

In the prior art, it is known to utilize a fluid for damping the oscillatory motion of a vibratory assembly within a galvanometer. Commonly, the adjustment of this fluid damping effect is achieved through the variation of the fluid level surrounding the vibratory assembly. This method of varying the damping fluid level requires exposure of portions of the vibratory assembly or coil above the level of the damping fluid in consequence of which such' galvanometer portions are exposed to an unequal thermodynamic potential, thereby creating hot spots within such portions of the coil. This has imposed serious limitations on the upper frequency at which the galvan0meter will operate. The effect of the coil hot spots can be minimized by the proper selection of coil parameters, but this necessarily results in a compromise in respect of the possible upper frequency limits. The increasing demand for galvanometers with improved frequency response as well as increased maximum frequency limitations has made impracticable the selectivity of galvanometer coil parameters.

For example, one means of increasing the maximum frequency output of a galvanometer may be accomplished by reducing the wire diameter which forms the galvanometer coil. This reduction of wire size will be accompanied by a corresponding increase in wire resistance which, in turn, increases the PR or power loss within the coil. The increased power loss is characterized by increased thermal energy within the coil which must be removed therefrom, in order to reduce coil hot spots. It, therefore, becomes obvious that the higher frequency outputs required by new galvanometers will be accompanied by an increased possibility of coil failure, unless the development of coil hot spot can be prevented. The reduction of galvanometer coil wire diameter removes the one parameter which in prior art devices could 'be adjusted for avoiding excessive coil heating. In order to eliminate the coil hot spots it becomes necessary to rely on external means, such as a cooling fluid, for removing the thermal energy from the coil. A proper selection of the damping fluid, therefore, should include a high thermal capacity as one of the important characteristics to be considered. Further, the galvanometer coil must be totally immersed in the cooling fluid for insuring complete elimination of hot spots.

I 3,404,342 Patented Oct. 1, 1968 However, when the vibratory assembly, including the coil, must be totally immersed in a damping fluid which also serves a cooling purpose, the means for adjusting the damping effect of said fluid through fluid level control is no longer available.

It is, therefore, one object of the present invention to provide a means for adjusting the galvanometer coil damping while maintaining the coil totally immersed in the damping fluid.

Another object of the instant invention is to provide a galvanometer capable of a high frequency output in which the damping fluid also functions more effectively as a cooling fluid for removing the thermal energy from the galvanometer coil while permitting a desired adjustability in the amount of damping provided.

Still another object of this invention is to reduce the error inherent in the high frequency response range of prior art galvanometers through an improved damping arrangement; a further object of the present invention is to provide such an improved galvanometer construction which at the same time allows a corresponding reduction of error in the low frequency response range.

A still further and more specific object of this invention is to provide an improved galvanometer damping arrangement which will allow the utilization of a lighter damping fluid thereby improving the overall frequency response range.

Other objects and many of the attendant advantages of the present invention will be better understood when considered in light of the following detailed specification and drawings, wherein:

FIG. 1 is an elevational view showing a galvanometer;

FIG. 2 shows an exploded elevational view of a galvanometer incorporating the present invention; and

FIG. 3 is a perspective cross-sectional view showing the galvanometer damping arrangement in greater detail.

Referring now to the drawings and, more particularly to FIG. 1, the galvanometer is shown generally at 10 wherein a tubular protective casing 12 is attached, as by a light press fit, to a tubular outer body 14. The tubular outer body 14 is comprised of a metallic tube, such as cupric nickel, in which the built-in pole pieces such as are customarily associated with galvanometer coils in prior art construction have been eliminated. This arrangement was fully disclosed in US. Patent No. 2,908,866, by C. A. Heiland et al., which issued Oct. 13, 1959, and is assigned to the same assignee as the present invention.

Extending through the longitudinal axis of the tubular outer body 14, FIG. 2, is a vibratory assembly 16 having a mirror 18 and a coil 20, located thereunder, and connected thereto by means of a suspension filament 22. A lower suspension filament 24 connects the opposite end of said coil 20 to a spool 26 carried on an anchor pin 28 which extends beyond said spool 26 and through a lower tubular support member 30. The lower tubular support member 30 is supported upon an internally relieved shoulder 31 in the lower end of the tubular outer body 14. The upper portion, or mirror 18, of the vibratory assembly 16 is connected bymeans of an upper suspension filament 32 to a spool 34 carried on an anchor pin 36. The anchor pin 36 passes through an upper insulated support member 38 having a reduced threaded portion extending upwardly along the longitudinal axis thereof. An upper end nut 42 is threada'bly attached to said upper support member 38 for providing a desired factory adjustment of the vibratory assembly within the galvanometer to the correct frequency and sensitivity. The inner surface of the outer tubular member 14 is internally relieved along its upper end forming a shoulder 43 upon which the end nut 42 rests. A retainer 44 is pressed into said relieved portion for retention of said end nut 42. A pin 45 passes through the upper insulated support member 38 and extends through mating elongated openings in the outer tubular body 14, thereby preventing the transmission of angular displacement to the vibratory assembly during the factory adjustment.

A pig-tail wire 46 connects the lower suspension filament 24 to a slip ring 47 which, as shown, is suitably mounted on an insulating member 48. The upper suspension filament 32 is connected by a pig-tail wire 50 to a slip ring 52, also mounted on member 48. The pig-tail 50 is carried to the upper suspension filament 32 through a groove, not shown, on the outer surface of the tubular outer body 14, passing thereinto through an aperture 54.

The lower tubular support member 30 has a reduced upper portion 56 which forms a cylindrical cavity with the inner surface of the outer tubular body 14 for receiving an inner tubular body 58 in coaxial arrangement therewith. The inner tubular body 58 is constructed from non-metallic material, such as glass tubing, having an inner bore of capillary dimensions. In the preferred embodiment of the present invention the inner tubular body 58 is utilized for allowing the outer tubular body 14 to be fabricated with openings therethrough, for reasons which will become obvious hereinbelow. The inner tubu' lar body 58 is filled with a damping fluid 60 to a level sufficient for totally immersing the coil 20 while avoiding contact with the mirror 18. The damping fluid 60 is retained within the inner tubular body 58 by capillary attraction. Said fluid 60, which totally immerses the coil 20, should have a high thermal capacity for removing suflicient thermal energy from the coil, thereby preventing coil hot spots. The damping fluid 60 may be one of many desirable types, such as silicone oil, which may be inserted into the inner tubular body by a conventional hypodermic syringe, not shown.

FIG. 3 shows the galvanometer .damping arrangement in greater detail. An adjustable tubular member 62 is coaxially arranged within the inner tubular body 58 for slidable movement along the bore of said inner body. The upper inner surface of the adjustable tubular member is outwardly relieved at 64 for receiving a rigid adjustment wire 66 which is attached thereto, as by soldering. The adjustment wire 66 is offset at 68 near its upper end for allowing easy contact with the inner surface of the outer tubular member 14. A slotted opening 70 through the side wall of the outer tubular member 14 allows access to the adjustment wire 66 for adjusting the tubular member 62. Once the proper location of the adjustable tubular member 62 is established the wire 66 is attached to the inner surface of the outer body 14, as by soldering.

The galvanometer assembly is completed by sliding the protective casing 12 over the outer tubular body 14 and aligning a rectangular opening 72 within the protective casing 12 for communicating with the mirror 18. An uppermost cap 74 is then pressed into the top portion of the protective casing 12 for closing the casing. An aperture76 within the cap 74 allows adjustment of the end nut 42. A kerf 78 is provided in the upper end of the cap 74 for providing a holding point from which rotational adjustment of the entire galvanometer assembly, about its longitudinal axis, may be obtained.

The adjustment of the galvanometer damping is achieved by varying the location of the adjustable tubular member 62 along the longitudinal axis of the tubular inner body 58 and coaxially about the vibratory assembly coil 20. Both the coil 20 and the adjustable member 62 are immersed within the damping fluid 60. The resistive force to the oscillatory motion of the coil 20 may be described in terms of fluid viscosity, surface area, coil frequency, and clearance between the coil 20 and the adjustable tubular member 62. Since the fluid viscosity and coil frequency remain constant when considering the damping force applied by the damping fluid, it becomes apparent that the variation of surface area and variation of clearance between coil and tubular member will vary the force which resists the oscillatory motion of the coil. Therefore, the raising or lowering of the adjustable tubular member, coaxially about the coil, difler entially varies the resistive force gradient which is reacting against the oscillatory motion of the coil and adjusts the damping of that coil.

While, in accordance with the provisions of the statutes, we have illustrated and described the best form of the invention now known to us, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention as set forth in the appended claims, and that in some cases certain features of the invention may sometimes be used to advantage without corresponding use of other features.

Having now described the invention, what is claimed as new and what is desired to be secured by Letters Patent is claimed as follows:

1. In a galvanometer of the fluid damped variety having a vibratory assembly, including a mirror and coil, extending through the longitudinal bore of a tubular outer body, the improvements which comprise:

a slidably adjustable tubular member coaxially arranged within said tubular outer body for surrounding a portion of said vibratory assembly, and

adjustment means for varying said adjustable tubular member along the longitudinal axis of said tubular outer body, whereby adjustment of said adjustable tubular member varies the volume of the space between said coil and said tubular outer body and thereby varies the damping of said vibratory assembly.

2. In a galvanometer of the fluid damped variety having a vibratory assembly, including a mirror and coil, extending through the longitudinal bore of a tubular outer body, the improvements which comprise:

a tubular inner body of capillary dimensions coaxially arranged within said tubular outer body, slidably adjustable tubular member coaxially arranged within said tubular inner body and surrounding portions of said vibratory assembly coil, whereby the adjustment of said adjustable tubular member along the longitudinal bore of said tubular inner body varies the volume of the space between said coil .and said tubular inner body and thereby varies the damping of said vibratory assembly.

3. In a galvanometer of the fluid damped type having a vibratory assembly, including a mirror and coil, extending through the longitudinal bore of a tubular outer body, the improvements which comprise:

a slidably adjustable tubular member coaxially arranged within said tubular outer body and formed for surrounding the lower portion of said vibratory assembly coil,

adjustment means for varying the position of said adjustable tube in coaxial relationship with said coil, .and

a damping fluid retained within said tubular outer body by capillary attraction fully immersing said vibratory assembly coil and characteristically having a high thermal capacity, whereby the adjustment of said adjustable tubular member within said damping fluid varies the fluid volume of the annular space between said coil and said tubular outer body and thereby varies the damping of said vibratory assembly.

4. In a galvanometer of the fluid damped variety having a vibratory assembly, including a mirror and coil, extending through the longitudinal bore of a tubular outer body, the improvements which comprise:

a tubular inner body of capillary dimensions coaxially arranged within said tubular outer body,

a slidably adjustable tubular member coaxially arranged within said tubular inner body for surrounding the lower portion of said vibratory assembly coil,

adjustment means attached to said adjustable tubular member for varying the position of said tubular member in coaxial relationship with said coil and for retaining said tubular member once adjusted, and

a damping fluid retained within said tubular inner body by capillary attraction fully immersing said vibratory assembly coil and characteristically having a high thermal capacity, whereby the adjustment of said adjustable tubular member within said damping fluid 5 References Cited UNITED STATES PATENTS 9/1951 Hoare et al. 10/ 1953 Richardson.

10 RUDOLPH V. ROLINEC, Primary Examiner.

P. A. URIBE, Assistant Examiner. 

1. IN A GALVANOMETER OF THE FLUID DAMPED VARIETY HAVING A VIBRATORY ASSEMBLY, INCLUDING A MIRROR AND COIL, EXTENDING THROUGH THE LONGITUDINAL BORE OF A TUBULAR OUTER BODY, THE IMPROVEMENTS WHICH COMPRISE: A SLIDABLY ADJUSTABLE TUBULAR MEMBER COAXIALLY ARRANGED WITHIN SAID TUBULAR OUTER BODY FOR SURROUNDING A PORTION OF SAID VIBRATORY ASSEMBLY, AND ADJUSTMENT MEANS FOR VARYING SAID ADJUSTABLE TUBULAR MEMBER ALONG THE LONGITUDINAL AXIS OF SAID TUBULAR OUTER BODY, WHEREBY ADJUSTMENT OF SAID ADJUSTABLE TUBULAR MEMBER VARIES THE VOLUME OF THE SPACE BETWEEN SAID COIL AND SAID TUBULAR OUTER BODY AND THEREBY VARIES THE DAMPING OF SAID VIBRATORY ASSEMBLY. 